1. Field of the Invention
The present invention relates to an image processing method and apparatus for a face image. More particularly, the present invention relates to an image processing method and apparatus for a face image in which the face image is extracted from an original image and a thresholded image of the face image can be produced with a high quality.
2. Description Related to the Prior Art
Various new techniques for service have been developed with wide use of the cellular phone. For example, there is a technique for uploading a face image recorded by use of a built-in camera of the cellular phone, and transforming the face image into a binary image of a simplified form. To this end, an image pickup condition for recording the face image must be limited and optimized for conditioning the production of the binary image, for example, limited property of the light amount of the background, color range and the like. It is very difficult to produce the binary image of an acceptable quality if the image pickup condition is unsuitable before recording the face image.
There are various known methods of thresholding or binarization. JP-A 2001-245148 discloses the thresholding of a local manner in which an original image contains a high density portion and a low density portion, and the low density portion is prevented from being thresholded with poor appearance upon occurrence of signal noise. JP-A 2001-222683 discloses an example of the thresholding in which an original image contains alphanumeric information with a shaded font, and signal noise derived from a blank portion of the image can be eliminated before producing the thresholded image.
Image pickup of the face image must be carried out in the optimized image pickup condition before the binary image or simplified image can be obtained. This is a problem in high difficulty in the image production. In the above suggested technique of the thresholding in which the linear discriminant analysis, it is highly difficult to produce the binary image neatly particularly if an image is a face image with finely distributed shading of surface texture.